Presbyopia is an age-related problem with near vision, due to progressive reduction in the eye's ability to focus, with consequent difficulty in reading at the normal distance. An effective refractive correction of presbyopia must provide simultaneous focus for far, intermediate, and near vision in all conditions of pupil sizes.
Diffractive intraocular lenses (IOLs) such as those described in U.S. Pat. No. 5,116,111 by Michael Simpson and John Futhey and in US 2006/0116764A1 by Michael Simpson can provide simultaneous bi-focus (far vision and near vision) correction for presbyopia, but have two inherent disadvantages: degraded night vision with night glare caused by light scattering at the junctions of diffractive zones in the lens surface, and a blind spot at intermediate distance between the far and near focus points.
Multifocal designs by controlling light distribution for far, intermediate, and near vision across different aperture size of a lens were proposed by Valdmar Portney in U.S. Pat. Nos. 5,225,858 and 6,557,998B2. These lens designs can perform better for intermediate vision than Simpson's diffractive IOLs, but are also known to be inferior for performance at near vision. Moreover, Portney's lenses fail to achieve their full potential as they are based on simple geometric ray tracing, without taking into account the diffraction effect of light propagation.
Aspheric lenses were also proposed in U.S. Pat. No. 6,923,539B2 by Michael Simpson and in U.S. Pat. No. 5,166,711 and U.S. Pat. No. 6,409,340B1 by Valdmar Portney. These lenses have a periodic refractive power distribution across a lens. While Simpson's lens can increase focus depth for a mono-focal lens as illustrated in FIG. 9 of U.S. Pat. No. 6,923,539B2, such lens is typically not suitable for presbyopic correction.
Spherical aberration across the pupil of an eye produces different focusing power at different pupil radii. Negative spherical aberration across pupil of an eye was proposed for mitigation of presbyopia by Seema Somani and Kingman Yee in U.S. Pat. No. 7,261,412 B2. There, the inventors noticed that negative spherical aberration across the entire pupil can shift the center of the focus range from far to an intermediate distance because negative spherical aberration produces focus power for far vision at the pupil center to intermediate vision at the pupil periphery.
However, inducing spherical aberration across an entire pupil of an eye has at least two limitations for presbyopic corrections. First, the total amount of spherical aberration induced across the pupil cannot be too strong to cause nighttime symptoms such as glare, halo and starburst, which is one of the fundamental reasons why lenses with significant spherical aberration has not been used in multifocal IOLs and contact lenses for presbyopic treatments. Second, Somani and Yee's method in U.S. Pat. No. 7,261,412 B2 is typically not sufficient for presbyoic treatments because the small amount of spherical aberration across the entire pupil only shifts the center of focus range and does not increase focus depth. Still further, currently known methods of spherical aberration for presbyopic corrections have failed to address issues of induced nighttime symptoms (glare, halo, starburst) and increase focus depth of an eye for far vision, intermediate vision and near vision, thus rendering such solutions less than desirable.
Consequently, although many configurations and methods for vision correction for treatment of presbyopia are known in the art, all or almost all of them suffer from one or more disadvantages. Thus, there is still a need to provide improved configurations and methods for vision correction for treatment of presbyopia.